In recent years, there has been strong demand for an automobile tire having a low fuel consumption property, in view of an environmental issue and a resource problem. Further, in view of safety, there has been demand for an automobile tire which is excellent in wet grip property, dry grip property, and driveability. A tire made from a rubber composition which contains silica as a filler is greater in low-heat buildup property than that of a tire made from a rubber composition containing generally-used carbon black. Accordingly, with the use of the rubber composition containing silica, it is possible to provide a tire having a lower fuel consumption property.
However, natural rubber and synthetic rubber having a low polarity, which is generally used as a material of a tire, is low in affinity for silica. For this reason, there has been known a technique of improving, by addition of various silane coupling agents, synthetic rubber or the like having a low polarity in affinity for silica. However, a rubber composition in which a silane coupling agent and silica are merely used together might be insufficient in abrasion resistance as compared with a rubber composition containing carbon black. Further, a silane coupling agent is expensive. For this reason, the greater a silane coupling agent content becomes, the higher a production cost becomes.
As a technique for solving these problems, there has been such a study that a specific denaturing agent is subjected to reaction so as to cause rubber itself to have affinity for silica. For example, Patent Literature 1 discloses such a conjugated diene rubber that a specific compound, having excellent affinity for silica, is reacted with an active terminal of a polymer. Further, Patent Literatures 2 and 3 disclose a rubber composition obtained in such a manner that (i) a conjugated diene rubber is obtained by causing a conjugated diene polymer having an active terminal to be reacted with polyorganosiloxane having a specific functional group, and (ii) silica is added to the conjugated diene rubber thus obtained. Furthermore, Patent Literature 4 discloses such a conjugated diene rubber that one of terminals of a molecular chain has an isoprene block and the other one of terminals of the molecular chain, which is an active terminal of a polymer, is reacted with specific tin halide compounds.